Such proportioners are typically based functionally on a device known in the industry by the term “eductor”. As used herein, an eductor is a device based on the principle of a venturi and is used to draw a metered amount of one fluid or chemical into a flowing stream of another fluid, frequently called a diluent, and such as water. This produces a mixed water and chemical in a discharging diluted effluent. Basically, a venturi-type eductor comprises a major fluid or diluent flow path through which the diluent flows, at a velocity, to an orifice. The flow path in the eductor typically diverges or increases in cross-sectional dimension downstream from the orifice so that a pressure drop is attained in the downstream fluid emanating from the orifice. Such an area of divergence in the fluid path defined in the eductor can be referred to as a diffuser chamber or area. A chemical inlet port is disposed at or just downstream of the orifice in the flow path and in an area of the eductor which can be referred to as an injection area or chamber.
This chemical inlet port is operably connected to a selected chemical source. The reduced pressure in the diluent flow path at the chemical inlet port sucks chemical into the diluent where it is mixed in the diluent in the diverging flow path as the diluent flows downstream from the orifice in the diffuser chamber.
Thus, the chemical is “educted” or sucked into the diluent flow path in a ratio to the diluent which is dependent on the parameters of the chemical flow path to the chemical inlet port, the cross-sectional configuration of that port, the viscosity of the chemical, the velocity of the diluent and degree of pressure drop produced in the diverging flow path proximate and downstream of the diluent orifice.
While varied configurations of proportioners including such eductors have been used in dispensing diluted chemicals, they have been attended by certain operational and performance limitations. In order to understand these problems in detail, it is important to consider several operational parameters of the simple or typical eductors used in such proportioners as described above.
When a pressurized fluid or diluent such as water enters the eductor inlet, it is constricted toward the orifice. As the water passes the orifice, it becomes a high velocity jet stream. The increase in velocity through the injection chamber results in a decrease in pressure, thereby enabling a second fluid, such as a cleaning chemical, to be drawn into the injection chamber and diluent through the chemical inlet. As the water/chemical mix travels through the diffuser chamber, the velocity is reduced and it is reconverted into pressure energy but at a pressure level lower than the pressure at the orifice.
Such a prior eductor is diagrammatically shown for illustration purposes in FIG. 1.
Such eductors, when used in industry as injector or jet pumps, usually are submerged or have the diffuser below water level. On the other hand, eductors used in the chemical dispensing industry have diffusers which are not submerged or “flooded” at initial startup.
A typical eductor used in the chemical dispensing industry will nevertheless operate as described above if the following conditions are met:
1. The orifice diameter must be smaller than the diffuser diameter. A device with the diffuser being smaller than the orifice will cause positive pressure at the chemical inlet. This could cause the diluent fluid, and any other component therein, to back flow into the otherwise unadulterated chemical source in a reverse direction through the chemical inlet port.
2. The eductor must be allowed to “flood” at startup. This “flooding” causes the diffuser portion to fill with liquid thus reducing the velocity of the incoming fluid. If no “flooding”, there is insufficient pressure drop to initiate and continue the necessary negative pressure to draw or suck chemical through the chemical inlet port into the injection chamber and the diluent fluid.
FIG. 2 shows a stream of water flowing through the typical non-flooded prior eductor of FIG. 1. The fluid flows through the orifice and continues undisturbed through the mixing chamber and diffuser from which it discharges to the atmosphere. Such a “non-flooded” eductor will not draw chemical through the chemical inlet, because the velocity of the water is not being reduced in the diffuser portion and injection chamber and there is no pressure reduction to initiate and then continue suction of the chemical through the chemical inlet port.
There are many ways that flooding can be accomplished. The Figures herein show several.
FIG. 3 shows a typical eductor having a discharge tube with a flooding ring located below the diffuser in the tube. In operation, water exits the orifice, travels through the diffuser and into the discharge tube where the stream impinges on a bar or other structure of the flooding ring. This causes the fluid to change direction, to back up and to cause a pressure drop. This floods the diffuser section, thus reducing the water diluent velocity. Pressure is reduced and this creates a vacuum at the chemical inlet.
In FIG. 4, a ramped deflector is added to the eductor to cause pressure drop in the diffuser section. Water in the stream impinges on the deflector. This interrupts the fluid jet from the orifice and causes the diffuser to “flood” so that a vacuum is created at the chemical inlet port.
Many schemes may be used to accomplish the flooding. The diffuser and orifice may be eccentric or the diffuser or orifice may be at an angle to one another.
The amount of back pressure in the diffuser portion of the eductor must also be controlled by the added water flow disruption feature. If the feature is not pronounced enough, then at low pressures the diffuser section will not flood. If the feature is too restrictive, there will be excessive back pressure and the eductor performance will be diminished. In extreme cases, if the flow is too high, there will be a positive pressure in the chemical inlet, in which case fluid will reverse flow through the chemical inlet.
Returning now to the function of proportioners used in the chemical dispensing industry, such as in dispensing diluted chemicals for cleaning purposes, and to enhance and facilitate a cleaning use, it is frequently desirable to provide mixtures of water and the same chemical in different dilute strengths or ratios.
In the past, a variety of selector valve and proportioner configurations have been used to these ends. Prior units have been, however, attended by certain operational and performance limitations as stated above. For example, cross-contamination by either residual chemicals in discharge passageways or by potential residual chemical intrusion into a feeding or discharge passageway of another chemical can contaminate the effluent.
One solution to this problem has been to provide independent and distinct proportioners for each chemical or dilute ratio with a separate discharge tube. Cross-contamination is reduced or eliminated, yet the number of discharge tubes is multiplied and the overall dispenser is large.
Another solution has been to use a single diluent valve feeding distinct chemical proportioners, or a single diluent input with a valve selectively coupling one of a plurality of chemical inlets to a single diluent stream or proportioner through varied flow regulating orifices to control the diluted mixture ratio. In some cases, a diluent flush channel is provided to cleanse internal passages of residual and undesirable chemicals precedent to a changeover. These features add parts, require space and cost, and complicate operations of the dispenser.
Accordingly, it is one objective of the invention to selectively provide dispensing of multiple chemicals or multiple chemical mixture ratios, or both, in a small package with no significant chemical contamination in any discharge.
A further objective of the invention has been to provide a proportioner for multiple chemicals or chemical ratios but in a small dilute proportioner apparatus.
A further objective of the invention is to provide a proportioner for multiple chemicals or chemical ratios flowing from a single discharge tube.
The use of a single discharge tube receiving mixture flow from multiple proportioners and eductors, however, is attended by a confining set of opposed performance parameters. On one hand, the flow parameters of one chemical cannot be such as to create a venturi effect as would draw chemical from chemical sources serving other proportioners discharging into the same tube. On the other hand, those parameters cannot create such back pressures as to pressurize non-selected proportioners with selected dilute chemical mixture in a way to contaminate the non-selected chemical source.
Accordingly, and stated in another way, if multiple eductors flow into one common discharge tube, there are at least two operational problems. On one hand, the pressures generated by one active eductor may be of such magnitude that the discharge back flows into one or more inactive eductors, contaminating the associated, non-selected chemical source. On the other hand, the pressures generated by one active eductor may be of such effect as to create a pressure differential sufficient to draw chemical from an inactive, non-selected chemical source, into the select dilute stream, thus contaminating it.
Thus, the objective of a proportioning dispenser for multiple chemicals or chemical ratios in a yet small proportioning device is difficult to attain.
It is, nevertheless, a further objective to provide an improved proportioner for producing multiple chemicals or chemical ratios from a common or single discharge tube without drawing non-selected chemicals into the diluent stream and without contaminating a non-selected chemical source by reverse diluent or selected chemical flow thereto.